nuttcp is a network performance measurement tool intended for use by
network and system managers. Its most basic usage is to determine the
raw TCP (or UDP) network layer throughput by transferring memory buffers
from a source system across an interconnecting network to a destination
system, either transferring data for a specified time interval, or
alternatively transferring a specified number of bytes. In addition
to reporting the achieved network throughput in Mbps, nuttcp also
provides additional useful information related to the data transfer
such as user, system, and wall-clock time, transmitter and receiver
CPU utilization, and loss percentage (for UDP transfers).

nuttcp is based on nttcp, which in turn was an enhancement by someone
at Silicon Graphics (SGI) on the original ttcp, which was written by
Mike Muuss at BRL sometime before December 1984, to compare the performance
of TCP stacks by U.C. Berkeley and BBN to help DARPA decide which version
to place in the first BSD Unix release. nuttcp has several useful features
beyond those of the basic ttcp/nttcp, such as a server mode, rate limiting,
multiple parallel streams, and timer based usage. More recent changes
include IPv6 support, IPv4 multicast, and the ability to set the maximum
segment size or TOS/DSCP bits. nuttcp is continuing to evolve to meet
new requirements that arise and to add desired new features. nuttcp has
been successfully built and run on a variety of Solaris, SGI, and
PPC/X86 Linux systems, and should probably work fine on most flavors
of Unix. It has also been used successfully on various versions of
the Windows operating system.

There are two basic modes of operation for nuttcp. The original or
classic mode is the transmitter/receiver mode, which is also the way
the original ttcp and nttcp worked. In this mode, a receiver is first
initiated on the destination host using "nuttcp -r", and then a
transmitter must be started on the source host using "nuttcp -t".
This mode is somewhat deprecated and is no longer recommended for
general use. The preferred and recommended mode of operation for
nuttcp is the new client/server mode. With this mode, a server is
first started on one system using "nuttcp -S" (or "nuttcp -1"),
and then a client may either transmit data to (using "nuttcp -t")
or receive data from (using "nuttcp -r") the server system. All
the information provided by nuttcp is reported by the client, including
the information from the server, thus providing a full snapshot of both
the transmitter and receiver ends of the data transfer.

The server may be started by a normal, non-privileged user by issuing
either a "nuttcp -S" or a "nuttcp -1" command. However, the optimal
and recommended method of running a server is to run "nuttcp -S" via
the inetd/xinetd daemon. This method has several significant advantages,
including being more robust, allowing multiple simultaneous connections,
and providing for access control over who is allowed to use the nuttcp
server via the hosts.allow (and hosts.deny) file. By default, the
nuttcp server listens for commands on port 5000, and the actual nuttcp
data transfers take place on port 5001.

The
host parameter must be specified for the transmitter, and provides the
host name or IP address of the receiver. In classic transmitter/receiver
mode, the
host parameter may not be specified for the receiver. In client/server mode,
when the client is the receiver, the
host parameter specifies the host name or IP address of the transmitter
(server).

Normally, a nuttcp data transfer is memory-to-memory. However, by
using the "-s" option, it is possible to also perform memory-to-disk,
disk-to-memory, and disk-to-disk data transfers. Using the "-s" option
with the transmitter will cause nuttcp to read its data from the
standard input instead of using a prefabricated memory buffer,
while using the "-s" option on the receiver causes nuttcp to write
its data to standard output. All these types of data transfers are
possible with the classic transmitter/receiver mode. For security
reasons, the "-s" option is disabled on the server, so it is not
possible to access the disk on the server side of a data transfer.

Print out a usage statement. Running nuttcp with no arguments will
also produce a usage statement.

-V

Prints the nuttcp version number. The nuttcp version is also printed
as part of the normal nuttcp output when the "-v" verbose output is
used (but not when using the default brief output). In client/server
mode, the version number of both the client and server is identified.

-t

Indicates that this nuttcp is the transmitter. In client/server mode,
this means the server specified by the
host parameter is the receiver.

-r

Indicates that this nuttcp is the receiver. In client/server mode,
this means the server specified by the
host parameter is the transmitter.

-S

Indicates that this nuttcp is the server. The only option that may
be specified to the server is the "-P" option, which allows one to
change the control port used by the server, but only when the server
is started by a normal, non-privileged user. When the server is
initiated by inetd/xinetd, the server control port should be specified
in the
services file.

-1

Basically the same as the "-S" option, but indicates a one-shot server,
i.e. the server exits after the first data transfer initiated by a
client. The "-1" option should only be used when the server is started
by a normal, non-privileged user. This option will probably rarely
need to be used, but can be useful for a quick test and eliminates
the possibilty of leaving a non-access controlled nuttcp server running
on the system (which can happen when using the "-S" option and forgetting
to kill the nuttcp server after finishing a series of tests).

-b

Produce brief one-line output, which includes the amount of data
transferred in MB (1024**2 bytes), the time interval in seconds,
the TCP (or UDP) network throughput in Mbps (millions of bits per
second), the transmitter and/or receiver CPU utilization, and for
UDP data transfers also outputs the loss percentage. In client/server
mode, most of the printed statistics are from the viewpoint of the
receiver. This is the default output format.

-B

This option is only valid for the receiver, and forces the receiver
to read a full buffer (as specified by the "-l" buffer length option)
from the network. It is mainly intended to be used with the "-s"
option to only output full buffers to standard output (e.g. for use
with tar). It is also implicitly set whenever the number of streams
as specified by the "-N" option is greater than 1. This option is
not passed to the server.

-d

For TCP data transfers, sets the SO_DEBUG option on the data socket.
This option is not passed to the server. It is a rarely used option
which may possibly be removed or renamed in a future version of nuttcp.

-D

This option is only valid for the transmitter, and only for TCP data
transfers, in which case it sets the TCP_NODELAY option on the data
socket, which turns off the Nagle algorithm causing data packets to
be sent as soon as possible without introducing any unnecessary delays.
This option is not passed to the server. It is a rarely used option
which may possibly be removed or renamed in a future version of nuttcp.

-s

Setting the "-s" option causes nuttcp to either read its data from
standard input rather than using prefabricated memory buffers (for
"nuttcp -t"), or to write its data out to standard output (for
"nuttcp -r"). The "-s" option is disabled for security reasons
on the server.

-u

Use UDP for the data transfer instead of the default of TCP.

-v

Verbose output that provides some additional information related to
the data transfer. In client/server mode, the server is always verbose
(implicit "-v" option), but the client controls the extent and type of
output via the "-v" and "-b" options.

-cdscp_value

Sets the socket option to support COS. Either takes a dscp value or
with the t|T modifier it takes the full TOS field.

-lbuffer_len

Length of the network write/read buffer in bytes for the
transmitter/receiver. It defaults to 64 KB (65536) for TCP data
transfers and to 8 KB (8192) for UDP. For client/server mode, it
sets both the client and server buffer lengths.

-nnum_bufs

Specifies the number of source buffers written to the network
(default is unlimited), and is ignored by the receiver. For client/server
mode, if the client issues a "nuttcp -r" command making it the
receiver, this parameter is passed to the server since the server
is the transmitter in this case. This parameter is also ignored
if the "-s" parameter is specified to the transmitter.

-wwindow_size

Indicates the window size in KB of the transmitter (for "nuttcp -t")
or receiver (for "nuttcp -r"). Actually, to be technically correct,
it sets the sender or receiver TCP socket buffer size, which then
effectively sets the window size. For client/server mode, both the
transmitter and receiver window sizes are set. The default window
size is architecture and system dependent. Note recent Linux systems,
out of a misguided desire to be helpful, double whatever window size
is actually specified by the user (this is not a bug with nuttcp but
a bug/feature of the Linux kernel). Also, with these Linux systems,
the actual window size thats used on the intervening network, as
observed with tcpdump, is greater than the requested window size,
but less than the doubled value set by Linux.

-wsserver_window

For client/server mode, the "-ws" option provides a mechanism for
setting a different window size on the server than the client window
size as specified with the "-w" option.

-wb

Normally, to conserve memory, the transmitter only sets the TCP send
socket buffer size and the receiver only sets the TCP receive socket
buffer size. However, if the "-wb" option is used, the transmitter
will also set the TCP receive socket buffer size and the receiver will
also set the TCP send socket buffer size. Under normal circumstances,
this should never be necessary. This option was implemented because
certain early braindead Solaris 2.8 systems would not properly set
the TCP window size unless both the TCP send and receive socket buffer
sizes were set (later Solaris 2.8 systems have corrected this deficiency).
Thus the b in this option can stand either for "braindead" or "both".

-pdata_port

Port number used for the data connection, which defaults to port 5001.
If multiple streams are specified with the "-N" option, the "-p" option
specifies the starting port number for the data connection. For example,
if four streams are specified using the default data connection port
number, nuttcp will use ports 5001, 5002, 5003, and 5004 for the four
TCP (or UDP) connections used to perform the data transfer.

-Pcontrol_port

For client/server mode, specifies the port number used for the control
connection between the client and server, and defaults to port 5000.
On the server side, the "-P" option should only be used when the server
is started manually by the user. If the server is started by inetd/xinetd
(the preferred method), the control connection must be specified by adding
a nuttcp entry to the
services file.

-Nnum_streams

Species the number of parallel TCP (or UDP) data streams to be used for
the data transfer, with the default being a single data stream. The
maximum number of parallel data streams that can be used is 128. If the
number of streams is greater than one, the "-B" option is implicitly set.
The current implementation does not fork off separate processes for each
data stream, so specifying multiple streams on an SMP machine will not
take advantage of its multiple processors. Of course it is always possible
to run multiple nuttcp commands in parallel on an SMP system to determine
if there is any advantage to running on multiple processors. This is
especially simple to do when running in client/server mode when the server
is started from the inetd/xinetd daemon. When running multiple nuttcp
commands in parallel, the "-T" transmitter timeout option may be used
to insure that all the nuttcp commands finish at approximately the same
time.

-Rxmit_rate_limit[m|g]

The transmitter rate limit throttles the speed at which the transmitter
sends data to the network, and by default is in Kbps, although the m
or g suffix may be used to specify Mbps or Gbps. This option may be
used with either TCP or UDP data streams. Because of the way this option
is currently implemented, it will consume all the available CPU on the
transmitter side of the connection so the "%TX" stats are not meaningful
when using the rate limit option. By default the rate limit is applied
to the average rate of the data transfer in real time, and not in CPU
time, so if nuttcp is switched out of the processor for any reason, when
it is switched back in, it is possible that the instantaneous rate may
momentarily exceed the specified value. There is an i qualifier to
the rate limit option (specified as "-Ri") that will restrict the
instantaneous rate at any given point in time to the specified value,
although in this case the final rate reported by nuttcp may be less
than the specified value since nuttcp wont attempt to catch up if other
processes gain control of the CPU. The default is no rate limit. Note
another way to throttle the throughput of TCP data streams is to reduce
the window size.

-Txmit_time_limit[m]

Limits the amount of time that the transmitter will send data to the
specified number of seconds, or number of minutes if the m suffix
is used. Normally a data transfer will either specify a fixed amount
of data to send using the "-n" option, or a fixed period of time to
send using the "-T" option. However, if both the "-n" and "-T" options
are used, the data transfer will be stopped by whichever option takes
affect first. The default is a 10 second time limit for the data
transfer.

Developed by Bill Fink based on nttcp which in turn was an enhancement
of the original ttcp developed by Mike Muuss at BRL. IPv6 capability
and some other fixes and enhancements contributed by Rob Scott. Many
useful suggestions and testing performed by Phil Dykstra and others.